The long-range goal of the proposed research is to identify molecular targets in sphingolipid signaling pathways for the development of therapeutics to treat cancer. The focus of the present proposal is the signaling enzyme sphingosine kinase-1, which produces the potent second messenger, sphingosine-1-phosphate. Sphingosine kinase represents a candidate target for cancer therapy. This concept is based on the observations that sphingosine kinase is overexpressed in many tumors and that experimental overproduction of sphingosine kinase transforms cells from a growth-controlled state to a tumorigenic state. The localization of sphingosine kinase to distinct intracellular sites is key to its ability to transform cells. The proposed experimental plan will determine why localization is important for transformation. This will form the basis for a discovery of novel molecular targets involved in the transforming ability of sphingosine kinase. To accomplish this goal, three specific aims are proposed. Specific Aim 1. Determine the activation-dependent subcellular localization of sphingosine kinase and sphingolipid metabolites affected by SK activity. Specific Aim 2. Determine the role of SK localization in cellular transformation and protumorigenic pathways. Specific Aim 3. The plasma membrane sphingosine-1-phosphate transport mechanism. Determine the mechanism and functional effects of enhanced sphingosine-1-phosphate secretion by activation of hSK-1.